本文主要介绍Android4.4默认Home应用Launcher3的启动过程和Launcher3的数据加载过程。Launcher的启动是开机时，ActivityManagerService准备好后开始的，下图是它的启动序列图：

step1，SystemServer中，ActivityManagerService准备好了。

step3，

    boolean resumeTopActivitiesLocked(ActivityStack targetStack, ActivityRecord target,
            Bundle targetOptions) {
        if (targetStack == null) {
            targetStack = getFocusedStack(); //获得mHomeStack
        }
        boolean result = false;
        for (int stackNdx = mStacks.size() - 1; stackNdx >= 0; --stackNdx) {
            final ActivityStack stack = mStacks.get(stackNdx);
            if (isFrontStack(stack)) {
                if (stack == targetStack) {
                    result = stack.resumeTopActivityLocked(target, targetOptions);
                } else {
                    stack.resumeTopActivityLocked(null);
                }
            }
        }
        return result;
    }

step6，

   boolean startHomeActivityLocked(int userId) {
        if (mHeadless) {
            // Added because none of the other calls to ensureBootCompleted seem to fire
            // when running headless.
            ensureBootCompleted();
            return false;
        }
        Intent intent = getHomeIntent(); //HOME intent
        ActivityInfo aInfo =
            resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);//查找home应用信息
        if (aInfo != null) {
            intent.setComponent(new ComponentName(
                    aInfo.applicationInfo.packageName, aInfo.name));
            // Don't do this if the home app is currently being
            // instrumented.
            aInfo = new ActivityInfo(aInfo);
            aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);
            ProcessRecord app = getProcessRecordLocked(aInfo.processName,
                    aInfo.applicationInfo.uid, true);//home应用未启动，返回null
            if (app == null || app.instrumentationClass == null) {
                intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
                mStackSupervisor.startHomeActivity(intent, aInfo); //step7
            }
        }

        return true;
    }

    Intent getHomeIntent() {
        Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);
        intent.setComponent(mTopComponent);
        if (mFactoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL) {
            intent.addCategory(Intent.CATEGORY_HOME);//Home应用的标志
        }
        return intent;
    }

的step14之后的过程。

step11~step14，开始异步加载应用图标，工作线程sWorkerThread。

step15~step20，加载workspace的图标，step16读取LauncherProvider的Favorites数据，favorites表的数据是Launcher数据库创建时从default_workspace.xml解析读取的。step18绑定图标信息。

step22，睡眠等待空闲进程，然后加载主菜单的所有app图标。

step23，从睡眠中醒来，准备加载所有app图标，包括widget等。

step24，

        private void loadAllApps() {
            final long loadTime = DEBUG_LOADERS ? SystemClock.uptimeMillis() : 0;
            .....
            final PackageManager packageManager = mContext.getPackageManager();
            final Intent mainIntent = new Intent(Intent.ACTION_MAIN, null); //在PackageManagerService查询所有要显示在桌面上的app
            mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);

            // Clear the list of apps
            mBgAllAppsList.clear();

            // Query for the set of apps
            final long qiaTime = DEBUG_LOADERS ? SystemClock.uptimeMillis() : 0;
            List<ResolveInfo> apps = packageManager.queryIntentActivities(mainIntent, 0);
            if (DEBUG_LOADERS) {
                Log.d(TAG, "queryIntentActivities took "
                        + (SystemClock.uptimeMillis()-qiaTime) + "ms");
                Log.d(TAG, "queryIntentActivities got " + apps.size() + " apps");
            }
            // Fail if we don't have any apps
            if (apps == null || apps.isEmpty()) {
                return;
            }
            // Sort the applications by name
            final long sortTime = DEBUG_LOADERS ? SystemClock.uptimeMillis() : 0;
            Collections.sort(apps,
                    new LauncherModel.ShortcutNameComparator(packageManager, mLabelCache));//按应用名称排序

            // Create the ApplicationInfos
            for (int i = 0; i < apps.size(); i++) {
                ResolveInfo app = apps.get(i);
                // This builds the icon bitmaps.
                mBgAllAppsList.add(new AppInfo(packageManager, app,
                        mIconCache, mLabelCache));
            }

            // Huh? Shouldn't this be inside the Runnable below?
            final ArrayList<AppInfo> added = mBgAllAppsList.added;
            mBgAllAppsList.added = new ArrayList<AppInfo>();

            // Post callback on main thread
            mHandler.post(new Runnable() {
                public void run() {
                    final long bindTime = SystemClock.uptimeMillis();
                    final Callbacks callbacks = tryGetCallbacks(oldCallbacks);
                    if (callbacks != null) {
                        callbacks.bindAllApplications(added); //step26，绑定
                        if (DEBUG_LOADERS) {
                            Log.d(TAG, "bound " + added.size() + " apps in "
                                + (SystemClock.uptimeMillis() - bindTime) + "ms");
                        }
                    } else {
                        Log.i(TAG, "not binding apps: no Launcher activity");
                    }
                }
            });
        }

右键复制图片地址，在浏览器中打开即可查看大图。

Android4.4 Framework分析——Android默认Home应用Launcher3的加载过程分析